Resistivity and Hall Effect of EuS in Fields up to 140 kOe

The dc electrical resistivity ρ and Hall effect were measured in n-type EuS single crystals. Data were taken from 300 to 2 K in magnetic fields H up to 140 kOe. At room temperature all samples had resistivities of the order 10^-2 {Ω}cm and contained n~10¹⁹ conduction electrons/cm³. Negative magnetoresistance was observed at all temperatures. At 77 K the negative magnetoresistance was due mostly to an increase in the mobility μ, although a small increase in n with increasing H was also observed. The zero-field resistivity as a function of temperature T exhibited a very large peak near the Curie temperature TC19 K. The data are consistent with the interpretation that this peak was due largely to a decrease in μ. In the presence of a magnetic field the resistivity peak decreased in magnitude, became broader, and shifted to a higher temperature. A very large negative magnetoresistance was observed near TC. At moderate fields this negative magnetoresistance was due largely to an increase in μ, but at high fields the changes in μ and n were comparable. Well below TC, the resistivity and Hall coefficient exhibited hysteresis as a function of H, and were constant at fields above magnetic saturation. In the field-increasing part of the hysteresis cycle ρ decreased monotonically with time. A resistivity "elbow," similar to the one observed earlier in Eu-rich EuO, was observed also in the Eu-rich EuS samples. With increasing H the elbow shifted to higher temperatures. Hall-effect measurements at 4.2 K indicated that at fields above magnetic saturation the anomalous Hall term was small compared to the normal term. The Hall data also showed that a large part of both the hysteresis in ρ and the resistivity elbow were due to a change in n. The various data are compared with theoretical models and earlier electrical-transport measurements on the Eu chalcogenides.